THIS invention relates to a method of routing transmissions within a multi-station network, typically between mobile stations in a cellular network utilising ad hoc or opportunistic message routing.
Such cellular systems consist of two primary families, namely Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems or hybrids of these two methods of duplexing. In the TDD system, base stations and mobiles achieve duplex or two-way communication through transmitting and receiving in sequential time slots, whereas in FDD duplexing is achieved by transmitting and receiving in different frequency bands.
In an ideal telecommunications system the minimum amount of transmit power would be used to cover a given path. In wireless telecommunications systems serving a large number of subscribers, an opportunistic method of transmission can be utilised, wherein information is relayed between a number of stations or nodes from an originating station to a destination station. An example of such a method is described in International patent application no. WO 96/19887 the contents of which are incorporated herein by reference.
In a system of the above kind, it has been shown that the most efficient method of communicating is to break a larger path down into a number of smaller hops, rather than to use a single relatively high powered hop. However, the efficient routing of data in such a system without incurring a large processing overhead is not trivial.
It is an object of the invention to address this issue.
According to the invention there is provided a method of relaying data between mobile stations in a cellular wireless communication system which comprises a plurality of mobile stations and a plurality of base stations, the method comprising the making of synchronisation transmissions from each base station within an area of coverage of the base stations, the synchronisation transmissions defining a broadcast control channel for the transmission of broadcast data from the base station to mobile stations within the area of coverage; receiving the synchronisation transmissions at mobile stations within the area of coverage and extracting data therefrom defining the broadcast control channel, and at least one calling channel on which mobile stations can transmit probe data to one another, the probe data being used by mobile stations to obtain connectivity information relating to the availability of other mobile stations.
The broadcast data transmitted from the base station to the mobile stations may contain information identifying the base station and information relating to available capacity at the base station.
The mobile stations may utilise the calling channel to broadcast probe signals to other mobile stations, the probe signals from each mobile station including information on the transmission power, local background noise level and path loss to other stations.
Preferably, mobile stations receiving probe signals from other mobile stations on the calling channel utilise the information therein to generate connectivity data relating to the other mobile stations.
The synchronisation transmissions preferably define at least one traffic channel usable by mobile stations to relay message data between themselves.
The synchronisation transmissions from the base stations are preferably made at relatively high power and a relatively low data rate, and message data transmitted between mobile stations on the traffic channel is transmitted at a relatively low power and a relatively high data rate.
In the method of the invention, high power, lower data rate transmissions are made by base stations which have wide area coverage and these transmissions are used for broadcasting synchronisation and other information directly to mobile stations within the cell (the area of coverage of the base station). The mobile stations operate at relatively low power and therefore need to relay message data from mobile station to mobile station to support high speed data services back to the base station from an originating mobile station within the cell. Relaying message data via mobile stations is also used to provide a high speed data service from the base station to a mobile station within the cell to effectively extend these services to the cell perimeter.
When mobile stations receive the synchronisation transmissions and broadcast data, they utilise this information to locate a specific time slot and frequency or xe2x80x9ccalling channelxe2x80x9d (also referred to as a random access channel or ORACH) usable by mobile stations to interact with one another.
The mobile stations transmit so-called broadcast probe messages on the calling channel which contain several parameters, such as transmission power, local background noise level and path loss data. This information allows a mobile station receiving a broadcast probe message from a neighbouring mobile station to derive a local connectivity indicator for that neighbour. Each mobile station maintains a list of local connectivity indicators for each neighbouring station. This neighbour list is included in broadcast probe messages sent out by each mobile station, so that on receiving a broadcast probe message including a neighbour list, a mobile station can derive local connectivity information for other mobile stations up to two hops away.
Mobile stations also include gradient information in their probe messages. The gradient information represents the cumulative cost of transmitting data via a number of relay links to a particular destination station. A cost function is used to calculate the gradient for a particular destination. This function will depend on a number of parameters such as the cumulative power required to reach a designated destination station, resource utilisation on relay links, the number of relays required, etc. Each mobile station will update the gradient associated with a particular destination station every time it receives a probe message from a neighbour containing the destination station""s identity data. As it is not practical for each mobile station to process and retain gradient information to every other mobile station, mobile stations use the synchronisation and broadcast transmissions from the base stations to identify which base station coverage area they are in, and develop gradients to those base stations. This significantly reduces the number of destinations that gradients are developed for, as normally a given mobile station will only be covered by one or a few base stations.
The synchronisation and broadcast information received from the base stations is used to define time slots and frequencies that can be used by mobile stations to transfer message data between themselves in relay mode. These time slots and frequencies are referred to as dedicated traffic channels (ODTCH).
The synchronisation of channels and resources is used by mobile stations according to the method of the invention to set up relay links to the base station more effectively.
The method of the invention is primarily aimed at utilising so-called ODMA (opportunity division multiple access) techniques in a cellular wireless communication system in order to enhance the performance of such a system. The system is thus a hybrid between a conventional cellular system in which mobile stations communicate directly to a base station within a cell, and a full ODMA system in which there is not necessarily any base station and mobile stations communicate with each other by relaying messages amongst themselves.
The basic call process of the present invention can be summarised as follows:
If a mobile station MSA wishes to initiate a call to a base station:
1. The initiating mobile station MSA initially sends notification on the calling channel (ORACH) to its neighbors informing them to start developing gradients back to it. All stations in the area of coverage of the same base stations as MSA (established by monitoring the synchronization and broadcast transmissions from the base stations) then start developing routing gradients to MSA to be used by the base stations to find routes to MSA.
2. The initiating mobile station MSA sends a call set-up probe message on the calling channel (ORACH) to one of its neighbours MSB after consulting its gradient table to determine the best route to the base station it is covered by. The call set-up probe contains details of the required bearer Quality of Signal (QoS) (Type of service such as Internet and message delay requirement) and throughput by the mobile for the call. This will determine how much resource will be reserved by the neighbor for the call.
3. The neighbour station MSB responds on the calling channel (ORACH) with an acknowledgement probe message containing the details of which Opportunity Driven Traffic Channel (ODTCH) channels may be used for the connection between MSB and MSA. If an ODTCH is available the ODTCH is used for all further call maintenance communications.
4. The same procedure is executed between MSB and one of its selected neighbours MSC, and then from MSC to its best neighbour. The gradients are followed from station to station until the base station is reached, and the call set-up information is passed on to the base station.
5. The call set-up information (request information) is passed on by the base station to the RRC (Radio Resource Controller), which negotiates with the core network providing authentication of the mobile station MSA for security and billing purposes and setting up of network resources. If the call is allowed by the network the relay link from the mobile to the network is effectively established.
6. The base station then needs to establish a relay link back to the mobile station MSA. Since the mobile station MSA initially sends notification on the calling channel (ORACH) to its neighbors informing them to start developing gradients back to it the base station waits for a timeout Troutewait for these gradients to reach it. After the timeout Troutewait the base station NodeB""s gradient table is examined for a suitable connect to the ODMA mobile station MSA. If the base station NodeB finds that mobile station MSC is its best neighbour for communication with mobile station MSA it will then begin a forward-relaylink bearer establishment procedure with MSC.
7. The same procedure is carried forward between MSC-MSB and MSB to MSA.
8. Once the forward-relaylink from the base station to MSA has been assigned the ODMA route has been established allowing data and further network system information to be exchanged.
9. Once the call is over the MSA removes from its probes the requirement for other mobile stations to develop gradients to it.
If the network wishes to initiate a call to a mobile station MSA:
1. Mobile stations monitor the synchronization and broadcast transmissions of base stations. When a mobile station detects that it has moved from the coverage of one base station to another it sends a location update to the base station. This can be done as a direct transmission to the base station or as a short message sent via relay. The location information is sent by the base station that receives it to a central mobile location data base that is used by the network to keep track of which base stations a mobile is covered by.
2. When the network wishes to initiate a call to a mobile station, the network consults a central mobile station location data base and decides which base stations the mobile is covered by. The network controller then tells these base stations to page the mobile.
3. Mobile stations monitor broadcast information from the base station. If a mobile station hears a page signal it will respond by initiating a call to the base station that it received the probe from. The mobile then informs its neighbors to start developing gradients back to it and initiates a call with the base station as described above in the mobile initiated call procedure.
4. After sending a page and optionally receiving a response message directly or via relay, the base stations wait for a time-out Twaitroute to allow sufficient time for routes to be gathered back from the paged mobile to the themselves.
5. The rest of the procedure is then identical to that used for a mobile initiated call.
Note that the procedure is almost identical to the mobile station originated case except that the call set-up procedure is invoked using a paging message from the network.
In this document, the following abbreviations and terminology are used:
Transport Channels
A general classification of transport channels is into two groups:
common channels (where there is a need for inband identification of the UEs when particular UEs are addressed) and
dedicated channels (where the UEs are identified by the physical channel, i.e. code and frequency for FDD and code, time slot and frequency for TDD).
Common transport channel types are:
Random Access Channel (RACH)
A contention based uplink channel used for transmission of relatively small amount of data, e.g. for initial access or non-realtime dedicated control or traffic data.
ODMA Random Access Channel (ORACH)
A contention based channel used in relaylink.
Forward Access Channel (FACH)
Common downlink channel without closed-loop power control used for transmission of relatively small amount of data.
Downlink Shared Channel (DSCH)
A downlink channel shared by several UEs carrying dedicated control or traffic data.
Broadcast Channel (BCH)
A downlink channel used for broadcast of system information into an entire cell.
Synchronization Channel (SCH)
A downlink channel used for broadcast of synchronization information into an entire cell in TDD mode.
Note that the SCH transport channel is defined for the TDD mode only. In the FDD mode, a synchronization channel is defined as a physical channel. This channel however should not be confused with the SCH transport channel defined above.
Paging Channel (PCH)
A downlink channel used for broadcast of control information into an entire cell allowing efficient UE sleep mode procedures. Currently identified information types are paging and notification. Another use could be UTRAN notification of change of BCCH information.
Dedicated transport channel types are:
Dedicated Channel (DCH)
A channel dedicated to one UE used in uplink or downlink.
Fast Uplink Signalling Channel (FAUSCH)
An uplink channel used to allocate dedicated channels in conjunction with FACH.
ODMA Dedicated Channel (ODCH)
A channel dedicated to one UE used in relaylink.
Logical Channels
The MAC layer provides data transfer services on logical channels. A set of logical channel types is defined for different kinds of data transfer services as offered by MAC. Each logical channel type is defined by what type of information is transferred.
A general classification of logical channels is into two groups:
Control Channels (for the transfer of control plane information)
Traffic Channels (for the transfer of user plane information)
The configuration of logical channel types is depicted in FIG. 1.
Control Channels
Control channels are used for transfer of control plane information only.
Synchronisation Control Channel (SCCH)
A downlink channel for broadcasting synchronisation information (cell ID, optional information) in case of TDD operation.
Broadcast Control Channel (BCCH)
A downlink channel for broadcasting system control information.
Paging Control Channel (PCCH)
A downlink channel that transfers paging information. This channel is used when the network does not know the location cell of the UE nor, the UE is in the cell connected state (utilizing UE sleep mode procedures).
Common Control Channel (CCCH)
Bi-directional channel for transmitting control information between network and UEs. This channel is commonly used by the UEs having no RRC connection with the network.
Dedicated Control Channel (DCCH)
A point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is established through RRC connection setup procedure.
ODMA Common Control Channel (OCCCH)
Bi-directional channel for transmitting control information between UEs.
ODMA Dedicated Control Channel (ODCCH)
A point-to-point bi-directional channel that transmits dedicated control information between UEs. This channel is established through RRC connection setup procedure.
Traffic Channels
Traffic channels are used for the transfer of user plane information only.
Dedicated Traffic Channel (DTCH)
A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for the transfer of user information. A DTCH can exist in both uplink and downlink.
ODMA Dedicated Traffic Channel (ODTCH)
A ODMA Dedicated Traffic Channel (ODTCH) is a point-to-point channel, dedicated to one UE, for the transfer of user information between UE""s. A ODTCH exists in relaylink.
1. Random Access Channel(s) (RACH) characterized by:
existence in uplink only,
limited data field. The exact number of allowed bits is FFS.
collision risk,
open loop power control,
requirement for in-band identification of the UEs.
2. ODMA Random Access Channel(s) (ORACH) characterized by:
used in TDD mode only (FDD is for FFS)
existence in relay-link
collision risk,
open loop power control,
no timing advance control
requirement for in-band identification of the UE.
3. Forward Access Channel(s) (FACH) characterized by:
existence in downlink only,
possibility to use beam forming,
possibility to use slow power control,
possibility to change rate fast (each 10 ms),
lack of fast power control and
requirement for in-band identification of UEs.
4. Broadcast Channel (BCH) characterized by:
existence in downlink only,
low fixed bit rate and
requirement to be broadcast in the entire coverage area of the cell.
5. Paging Channel (PCH) characterized by:
existence in downlink only,
possibility for sleep mode procedures and
requirement to be broadcast in the entire coverage area of the cell.
6. Synchronisation channel (SCH) characterised by:
existence in TDD and downlink only
low fixed bit rate
requirement to be broadcast in the entire coverage area of the cell
7. Downlink Shared Channel(s) (DSCH) characterised by:
existence in downlink only,
possibility to use beamforming,
possibility to use slow power control,
possibility to use fast power control, when associated with dedicated channel(s)
possibility to be broadcast in the entire cell
possibility for implicit identification of destination UE based on signalling on another channel (DCH or DSCH Control Channel).
8. DSCH Control Channel characterised by:
existence in downlink only,
possibility to use beam forming,
possibility to use slow power control,
lack of fast power control and
requirement for in-band identification of UEs.
Gateway UER/Seed
A ODMA relay node that also communicates with the UTRAN using either TDD or FDD mode.
ODMA Relay Node
A relay device, such as a UER or Seed, that is capable of relaying using the ODMA protocol.
Relay
A device capable of receiving and transmitting information for another user.
Relaying
The process of receiving and transmitting information for another user, such as carried out by a UER.
Relaylink
Relaylink is the communications line between two ODMA relay nodes.
Root Relay
ODMA relay node where communications are either sourced or sunk.
Seed
A ODMA relay node which is deployed by a network operator and is generally fixed, constantly powered, and has no display/keypad.
User Equipment Relay (UER)
A UE capable of relay operation and which may source and sink information.
An aim of the present invention is to provide a method and system wherein Mobile Originated (MO) and Mobile Terminated (MT) routing takes place in both a standard Time Division Duplex (TDD) system and in a TDD/FDD (Frequency Division Duplex) system.
Thus, according to the present invention, a method of integrating the relaying techniques between mobiles and base stations using TDD and FDD is provided. This invention makes use of opportunistic ad hoc routing techniques, as described in South African patent no. 95/10789, and uses the concept of power adaption described in South African patent no. 98/6882, and routeing techniques as described in South African patent no. 98/4891. The contents of these patents are incorporated herein by reference.
Effectively, the present invention involves a hybridisation of the systems disclosed in the above patents in order to enhance or implement the methodology described in South African patent no. 98/1835, the contents of which are incorporated herein by reference. This patent document, a cellular structure whereby base stations have regions of reduced available resources between them and rely on relaying by mobile stations in order to provide resources to these regions, thereby enhancing capacity and improving performance.
In order for mobile stations (mobiles) in the network to derive routes or methods of relaying information or data to and from the base stations, they probe and adapt their power and transmissions to gather a certain number of neighbours. This probing is done on an adaptive basis where the power level and the rate of probing and the interval between probing is set based upon the feedback from the other stations as described in South African patent no. 98/4891.
In this patent methods of generating gradients are also described, which consists of handing information from neighbour to neighbour as to the amount of power or quality of path to various destinations in the network. In this patent a technique is extended to a cellular structure where the base station, referred to as node xe2x80x9cBxe2x80x9d, is the primary route for which gradients must be found. This vastly simplifies routing, since providing mobiles are routing the majority of their information to and from the base stations, all a mobile has to do is generate gradients to the base station or node xe2x80x9cBxe2x80x9d. This is a simplified method to that described in patent no. 98/4891. In that application there was full mesh routing between any node to any node on a multi-hop basis. Therefore, in the context of a cellular environment, mobiles only need to probe and gather gradients to base stations in their normal idle environment. During this idle probing process, sufficient neighbours are gathered to allow at least one gradient to be found to the base station, preferably more, to allow redundant routing to be possible.
The present invention has particular application in an Opportunity Driven Multiple Access (ODMA) system. In such a system, xe2x80x9cneighbour gatheringxe2x80x9d is used to effect the routeing process within the network. Neighbour gathering is a process whereby the local connectivity of an ODMA relay node is assessed through the use of background probing messages. This neighbour information is stored within a neighbour table. Gradient tables are also derived from the neighbour messages but are used to evaluate the end-to-end connectivity. Gradients are effectively a cost function of the routeing messages over a particular path in terms of propagation conditions, number of hops, and other system parameters. In practice each mobile station should have at least one gradient to a NodeB which will allow any call set-up procedures to be executed allowing for route acquisition.
The simplest method of implementation of opportunity driven multiple access into a conventional cell phone infrastructure, would be to have the base stations perform the same functions as the mobiles, whereby they probe and gather neighbours and follow the same mechanisms as the mobiles, thereby allowing simple methods of routing to be used in that the base station node would appear to be the same as any other node in the network with the one provision that it would be routed to or gradients would be gathered to it from every other node within the region of the cell. In order to allow this, the base stations would need to operate in time division duplex to allow probing to be performed and monitoring of the same channel in the same way as the mobiles do. This method of using a calling channel is described more fully in South African patent no. 98/4891.
If the base station operates in time division duplex mode, then the features of paging whereby the base station can transmit and call any particular mobile to initiate transmission of traffic, as described in South African patent no. 98/1835. In addition, the base station can allow transmissions which can synchronise the various remotes to allow them to define time slots and intervals of transmission, thereby allowing more effective synchronisation of their local clocks and more efficient use of the resources. The base station broadcasts this time synchronisation information on, for example the calling channel or a dedicated broadcast channel, which is monitored by all the remotes in the network or in the region of the particular base station. This allows the mobiles or remotes to identify which base station they are being covered by and to synchronise themselves with respect to that base station and to each other. As shown in FIG. 1, the region of coverage of the base station broadcasts and low data rate coverage will cover the complete cell, while the region of higher resources covers only part of the cell using the methodology described in South African patent no. 98/1835.
One implementation of ODMA would be to use a TDD system that has all of the ODMA probing mechanisms and procedures built into the TDD infrastructure. This implementation results in system information such as synchronisation and paging messages being readily available from the standard TDD system. The mobile station originated and terminated ODMA call set-up procedures and the location update procedure are described below.
One of the aims of ODMA is to extend the range of the data coverage, e.g. to match that offered by TDD and FDD for speech coverage. A simplistic view of this concept is illustrated in FIG. 2.